settings-editor: Fix -Wcomma warning
Clang 19.1.7 reported a -Wcomma
warning:
[57/226] Compiling C object xfce4-settings-editor/xfce4-settings-editor.p/main.c.o
../xfce4-settings-editor/main.c:68:70: warning: possible misuse of comma operator here [-Wcomma]
68 | xfconf_channel_set_int (channel, "/last/window-width", width),
| ^
../xfce4-settings-editor/main.c:68:9: note: cast expression to void to silence warning
68 | xfconf_channel_set_int (channel, "/last/window-width", width),
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| (void)( )